1. Field of the Invention
The present invention relates to telemetry systems. More specifically, the present invention relates to pulse code modulation data transmission and decommutation systems.
While the invention is described herein with reference to an illustrative embodiment for a particular application, it is not limited thereto. Those of ordinary skill in the art, having access to the teachings provided herein, will recognize additional modifications, applications and embodiments within the scope of the present invention.
2. Description of the Related Art
In the development of sophisticated electromechanical systems, it is often necessary to transmit, receive, record and analyze data relating to the performance of the system in a laboratory or operational environment. Typically, this telemetry data is encoded prior to transmission, received, demodulated, and decoded for analysis. Pulse code modulation (PCM) encoding schemes are often used in this application.
In most PCM schemes, the received and demodulated data stream is synchronized to a local oscillator and input to a decommutator. The decommutator (DECOM) searches the synchronized data for a particular sync pattern. When the pattern is detected, the DECOM formats the data for input and analysis by computer. Unfortunately, the use of conventional DECOM units may be somewhat problematic.
First, the telemetry data from the DECOM unit must be transferred to the host computer via direct memory access (DMA). While this data is being written to a disk, new data must be accumulated in memory. This is also a DMA transfer, and it has been noted that two simultaneous DMA transfers make a typical minicomputer bus very busy. The level of additional activity in the host computer can lead to frequent system crashes. In the past, this problem was addressed by playing the recorded telemetry data back at half speed. However, this doubled the data acquisition time.
Secondly, some commercially available DECOMs provide interface cards which reside in the computer, as a substitute for the interface cards normally provided by the computer manufacturer. Often, these cards are found to violate the manufacturer's interfacing standards. This results in computer crashes, loss of data, and multiple test runs to acquire a single set of valid data. Noise generated within the DECOM, and transmitted over clock and control lines into the computer interface cards further contributes to the loss of data.
Thirdly, some commercially available DECOMs have minimal built-in-test `BIT` and diagnostics capability, for the DECOM and for the DMA interface cards. This often results in significant system down time.
Thus there is a perceived need in the art for an interfacing, between a DECOM and a host computer, that permits direct memory access without impairment of the operation of the computer; has a built-in-test capability; uses standard or recommended interfacing protocols; and has minimal noise susceptibility or adequate noise rejection capability.